The principal issues addressed in this proposal are: 1) whether motor processing within the basal ganglia-thalamocortical `motor circuit' is organized, at the neuronal level, in a predominantly serial or parallel fashion; and 2) whether there are systematic transformations, at successive stages of the circuit, in the neural representations of variables that have been implicated in different functional `levels' of motor processing. The proposed studies are designed to determine a) whether the same categories of information (i.e., the same motor variables) are proposed at different stages (cortical, striatal, pallidal, thalamic) of the `motor circuit'; b) whether there are systematic changes in the proportionate representation of a given motor variable by neurons at successive stages of the circuit; and c) whether there are systematic shifts, at successive stages of the circuit, in the regression slopes relating variable-specific changes in neuronal discharge rates to gradations in the represented variables. The Specific Aims for the project are as follows: [1] To determine whether, during the planning and execution of visually guided limb movements, multiple `levels' of motor processing are represented in parallel by neuronal activity within each of the precentral motor fields that contribute to the `motor circuit'. The activity of individual neurons in SMA, MC and APA will be recorded in monkeys performing tasks that require them to make reaching movements to position a cursor in two-dimensional space. The tasks involve both the preparation and execution `modes' of motor processing, and will also dissociate variables relevant to different `levels' of processing viz, target level variables, trajectory/kinematic variables, and dynamic/muscle-related variables. Data from the three areas will then be compared, based on results of both categorical and regression analyses. [2] To determine whether, during the planning and execution of visually guided limb movements, multiple `levels' of motor processing are represented in parallel by neuronal activity at the striatal stage of the `motor circuit'. Task-related single unit activity will be sampled from the arm region of the putamen in monkeys performing the same tasks employed in Specific Aim 1. After being subjected to the same set of analyses, the data will be compared with those obtained in Specific Aim 1. [3] To determine whether, during the planning and execution of visually guided limb movements, multiple `levels' of motor processing are represented in parallel by neuronal activity at the pallidal stage of the `motor circuit'. Task-related single unit activity will be sampled from the arm region of GPi in monkeys performing the same tasks used in Specific Aims 1 and 2. These data will be compared with those obtained in Specific Aim 2, in the same manner as the putamen and cortical data are to be compared. [4] To determine whether, during the planning and execution of visually guided limb movements, multiple `levels' of motor processing are represented in parallel by neuronal activity at the thalamic stage of the `motor circuit'. Task-related single unit activity will be sampled from the are region of VLo in monkeys performing the same tasks used in Specific Aims 1-3. These data will be subjected to the same analyses outlined above, and compared with both a) the SMA data from Specific Aim 1, and b) the GPi data from Specific Aim 3.